In the semiconductor industry, once electronic circuits are formed on semiconductor chips and the chips are packaged, it is necessary to completely test the package to ensure correct operation. Generally, the electronic circuits are formed in the semiconductor chip and the chip is attached to a lead frame or the like. The chip is then encapsulated with the leads extending straight out from the package in a common plane. In one prior art process, the circuitry within the package is tested at this time, because it is easier to contact the leads when they are in a common plane, and generally because it is difficult to make contact to preformed leads.
The major problem with this prior method is that the leads are formed after testing of the circuitry is completed. However, in many instances the process of forming the leads causes damage to the leads and, in some instances, can even cause the leads to be loosened from the chip and/or breakage of the encapsulation. Thus, it has become common to perform an open/short test after the lead forming process, which extends the manufacturing and testing procedure and increases the manufacturing costs. However, difficulty in contacting the formed leads applies also to this test. Further, intermittent wire bonds are impossible to detect because the pulling force on the leads that caused the wire bond failure has been relieved when the device left the forming station, which is the final assembly step, and no further testing is performed.
Because devices and packages are becoming smaller, it is becoming even more difficult to make reliable contact on the preformed leads. Contact failure on preformed leads is currently at about 0.5%. Excess contact pressure applied to the leads in an attempt to ensure a reliable electrical contact with the leads has a potential to deform the leads out of specification.
Accordingly, it is desirable to perform tests on semiconductor packages which reliably contact the leads and determine failures caused by formation of the leads.
It is a purpose of the present invention to provide a new and improved lead forming and package testing method.
It is another purpose of the present invention to provide a new and improved lead forming and package testing method in which constant and reliable contact with the leads is made.
It is a further purpose of the present invention to provide a new and improved lead forming and package testing method in which failures caused by lead formation can be determined.
It is still another purpose of the present invention to provide a new and improved lead forming and package testing method in which testing time and expense is reduced.
Yet a further purpose of the present invention is to provide a new and improved lead forming and package testing method which improves detection of lead forming induced failures, including intermittents.
A still further purpose of the present invention is to provide a new and improved lead forming and package testing method in which bending of the leads out of specification is substantially reduced and tested packages can be placed directly into final outgoing packages, i.e. tapes and reels.